Excessive daytime sleepiness (EDS) is widespread throughout the population, interfering with day-to-day activities, work, and relationships. EDS reduces productivity, concentration, memory, and can negatively impact on mood, and may cause danger to the community by those affected driving or operating machinery while drowsy.
Daytime sleepiness may be caused by an underlying medical condition such as sleep disordered breathing, by insufficient sleep resulting from poor sleep hygiene, self-imposed or socially dictated sleep deprivation, etc.
There have been attempts to quantify sleepiness, or to assess sleep quality.
Introspective behavioral scales and performance tests have been used to measure sleepiness and use subjective scales to query the individual's perception of alertness/sleepiness.
The Stanford sleepiness scale and Karolinska Sleepiness Scale assess the momentary degree of alertness/sleepiness. This is useful for a period but generally is less helpful in examining the global feelings of sleepiness. Also, in order to achieve accurate results, a subjective evaluation that is representative of the entire period between treatment sessions is needed.
The Epworth sleepiness scale (ESS) is a self-administered questionnaire used to determine the subject's general level of daytime sleepiness. Participants are asked to rate the likelihood that they would fall asleep in a range of common everyday situations. A rating of 0 means that the subject would never fall asleep compared to 3, meaning there is a high chance of dozing or falling asleep.
The summation of these ratings is the ESS score—an Epworth score of 0 is non-sleepy, 10 or more is considered sleepy, and 18 or more is very sleepy.
The Pittsburgh Sleep Quality Index (PSQI) is another method for determining sleep quality and sleep disturbances. The PSQI is a self-rated questionnaire which assesses sleep quality and disturbances over a 1-month time interval. Nineteen individual items generate seven “component” scores: subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleeping medication, and daytime dysfunction. The sum of scores for these seven components yields one global score. The higher scores generally correlated with greater sleep complaints and therefore diminished quality.
Another new method of measuring perceived sleepiness is to use pictorial scales which depict cartoon pictures of different degrees of tiredness.
Objective tests to measure sleepiness include Pupillography, the Multiple Sleep Latency Test (MLST), and Maintenance of Wakeful test.
Pupillography is based on changes in pupil stability that corresponds to the level of alertness. This technology is currently used in devices that are designed to prevent driver fatigue.
The Multiple Sleep Latency Test (MSLT) provides a valid measure of daytime sleepiness on the particular day of the test. This test is based on the premise that the sleepier the subject, the faster they will fall asleep when encouraged to do so while lying down in a non-stimulating environment (Johns 1991). The MSLT includes four to five opportunities to nap spaced across the day at 2-hour intervals. The MSLT is very cumbersome, time consuming, and expensive to perform, as it takes all day.
The Maintenance of Wakeful test is similar to the MSLT and asks patients to try to remain awake for as long as possible. It is currently used for legal purposes to determine if someone suffers from excessive daytime sleepiness.
However, for these methods to be useful tools for improving the patient's sleep, the patient must have insight into the problem and be able to distinguish between sleepiness from other factors affecting performance.
There have also been objective measurements of the patient's sleep quality.
In U.S. Publication No. 2005/0267362, an assessment of sleep quality and sleep disordered breathing is determined from cardiopulmonary coupling between two physiological data series—an R-R interval series derived from an electrocardiogram (ECG) signal, and an ECG-derived respiration signal.
In U.S. Pat. No. 6,120,441 (Griebel), various sensors detect a patient's body functions which are stored in a recorder. The stored data is then transferred to a computer where it is analyzed and evaluated.
U.S. Pat. No. 6,468,234 (Van der Loos et al.) describes a method and apparatus for measuring sleep quality that utilizes sensors incorporated in a sheet which is laid on top of a conventional mattress on which the subject sleeps, interface software for collecting user lifestyle data, and lifestyle correlation software for correlating the lifestyle data with the data acquired by said array of sensors.
U.S. Pat. No. 6,878,121 (Krausman et al.) describes a device which uses a motion sensor to measure the movement of a patients arm during sleep and then produces a sleep score based on these movements.
However, the existing arrangements can be improved upon in terms of sufficiency of measurement and feedback to the patient regarding their sleep.